The present invention is directed to a roller switch. Specifically, the invention is directed to a roller switch for sensing the leading edge of a material on a conveyor belt, which triggers a sensor to determine the length of the material on the conveyor belt.
In tire manufacturing, stock material of various types is applied to a building drum. The stock materials are cut to a required length. The cutting of the stock material occurs either at the building drum, or prior to arriving at the building drum. If the stock material is cut at the building drum, the strip length is determined by the tire builder or by a sensor. If the stock material is to be cut automatically, to reduce waste, the length of the stock must be accurately measured.
One method of measuring stock material is the roller switch illustrated in FIG 4. The roller switch, mounted along the side of a conveyor belt carrying the stock material, has a mounting bracket 102, a sensor bracket 104, a roller 106, and a flag arm 108. The roller 106, which extends only a partial distance across the conveyor, is related to the flag arm 108 and the related roller 106 and arm 108 pivot about a shaft 110. The flag arm 108 is formed of a lightweight material and is spring biased to maintain its position when the switch is not in operation. The side 112 of the flag arm 108 that is adjacent to a photoeye mounted within the sensor bracket 104 is covered in a reflective tape.
At the illustrated rest, or non-sensing, position, the flag arm 108 is not directly adjacent to the photoeye. When material travels under the roller 106, the roller 106 is pushed up, and due to the connection between the roller 106 and the flag arm 108, the flag arm 108 moves and the side of the arm 112 covered in reflective tape is then positioned adjacent to the photoeye. Due to the reflective taping on the flag arm 112, light is directed back to the photoeye and a sensor is triggered to indicate that material is now traveling under the roller 106 and measurement of the length of the material is taken.
While this roller switch has been sufficient, it has not proven to be reliable for extended periods of time due to the following problems. The photoeye is triggered by reflective tape; however, the tape can quickly become dirty and thus unreliable, requiring down time to clean the switch. The unit is also susceptible to being knocked out of adjustment. This can occur if the material traveling on the conveyor gets bunched up or is too thick and hits the roller 106. Additionally, if the thickness of the material is too great, the flag arm 112 may travel past the photoeye, providing an incorrect indication. Also, the switch is easily knock out of adjustment during the removal of stock. Stock is frequently removed from the conveyor for a variety of reasons.
The present invention is designed to overcome the limitations of the known mechanism. The roller switch is more robust than the known conventional roller switches.
The disclosed roller switch has a roller, a flag arm, and a photoelectric detector. The roller is connected to the flag arm and vertical movement of the roller causes the flag arm to move. The movement of the flag arm causes the photoelectric detector to send a signal. The signal may be used to measure the length of a material passing under the roller. The inventive roller switch has a pair of flag arms, and the roller is mounted on a shaft extending between the pair of flag arms. By providing a pair of flag arms connected by the roller, the roller switch is more robust and durable.
In one aspect of the invention, to further increase the robust character of the roller switch, a tube extending between the flag arms is located adjacent to the roller. When material passes under the roller switch, the material must first pass under the tube.
In another aspect of the invention, the vertical movement of the roller cause the upper end of the flag arm to unblock the photoelectric detector.
In another aspect of the roller switch, the roller switch is capable of pivoting about one end when mounted onto a support structure. Pivoting of the entire unit allows for easier servicing of the roller switch and makes it easier to remove any material from beneath the roller switch.
In another aspect of the roller switch, each flag arm is attached to an end plate. The first end plate is attached to pivoting means and the second end plate is attached to locking tube into which a locking pin is inserted. The roller switch pivots about the first end plate when the locking pin is removed from the tube.
Also disclosed is a method of measuring the length of a finite length strip material. The method includes the steps of placing the material on a moving conveyor belt, passing the material under a roller, causing the roller to vertically move, pivoting a flag arm in response to the movement of the roller, generating a signal in response to the movement of the flag arm, and measuring the length of the material. In the inventive method disclosed, the material passed under a tube prior to passing under the roller and the flag arm pivots about a shaft extending through the tube.